This gripper is known from WO 95/11518. In the known gripper the gripping claws are held by spring force in the position which holds the wafer-shaped article (wafer) so that the location of the wafer-shaped article (wafer) relative to the gripper is not unequivocally defined, because in the known gripper the conical spreading body no longer acts on the gripping claws as soon as the gripper holds a wafer-shaped article, therefore the gripping claws tightly adjoin the outside edge of the article. Often wafer-shaped articles (wafers) were not held centered to the gripper axis, especially when a flat or notch comes to rest on the edge of the wafer-shaped article in the area of one of the gripping claws. In this case this gripping claw cannot exert a force acting radially to the inside on the wafer-shaped article so that the gripping claw opposite it shifts the wafer-shaped articles out of the centered position under the action of the spring force loading it. For the case in which all gripping claws tightly adjoin the edge of the wafer-shaped article, when it is held with the known gripper, there are different holding positions since the spring constant of the individual springs which load the gripping claws to the inside are not exactly the same.
When wafer-shaped articles are placed on holders, for example, when silicon wafers are placed on chucks which hold the articles during further treatment steps (etching, polishing, etc.) the above described problems cause other problems in that the known gripper could place the wafer-shaped article exactly concentrically to the axis of rotation of the chuck only in exceptional cases, therefore rather randomly. For chucks which are equipped with (adjustable) pins on their surface facing the wafer-shaped article, which can move radially to the inside if necessary in order to center the wafer-shaped article (U.S. Pat. No. 5,513,668), this is not a problem since the wafer-shaped article has ultimately been centered. In chucks for wafer-shaped articles without the aforementioned pins in which the wafer-shaped articles are held exclusively or preferably by the Bernoulli principle (U.S. Pat. No. 4,903,717) or by negative pressure (WO 97/03457), for wafer-shaped articles which have not been concentrically placed, problems with unbalanced mass arise when the wafer-shaped article has been caused to rotate by the chuck during the treatment steps to be carried out.